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Posted: Nov 10, 2014

Counting stars 2.0

(Nanowerk News) In winter time, when nights become longer and darker, stargazing can be a fantastic experience and family activity. But in urban areas, the stars disappear behind the skyglow caused by waste light that shines up into the sky. This light pollution is not only a problem for astronomy. Scientists from the interdisciplinary project “Loss of the Night” study how it affects health, society, and the environment. In order to measure how skyglow is changing, they have developed an app for smartphones, which allows citizen scientists to count the number of visible stars in the night sky. The app, originally only available for Android, has now been expanded to support Apple’s iOS.

Screenshot of the “Loss of the Night” app.

Many people alive today have never seen the Milky Way, because in the cities where they grow up only a handful of stars and planets can be seen at all. But with newly developing technologies, like the LED lamps that were awarded the Nobel Prize this year that might change. “In recent decades, illumination increased at a rate of about 6% per year” says Dr. Franz Hölker, who studies artificial light at the Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB) in Berlin. “Changes in lighting systems could make the sky brighter or darker, depending on how they are implemented. Our app will help us to understand how the sky is changing worldwide.”

Stargazing for science

On November 10, the researchers released an updated version of their app, which allows participants to determine the number of visible stars in the night sky.

”The app works by interactively directing users to individual stars, and asking whether they can see the star or not”, explains Dr. Christopher Kyba of GFZ Potsdam. “By determining what the faintest visible star is, we know how many stars are visible at that location, and by extension how bright the sky is.”

No prior astronomical experience is necessary. “Before we developed the app, I only knew a few obvious constellations, like Orion. But by using the app I’ve learned lots of stars and constellations by name, without even trying to” said Kyba.

In addition to expanding support to iOS phones and four new languages, a number of improvements were made to the app. The most important change from the scientists’ perspective won’t actually be visible to users: an improved algorithm for suggesting stars that improves the precision of the observations and removes stars that users have had trouble with in the past. Other changes were made in response to feedback from the citizen scientists that use the app.

“The new version fits the user’s data and tells them approximately how many stars are in the sky immediately after the observation is completed, as well as how consistent their observations were”, says Kyba.

The researchers say that citizen science is the only currently available method to track global changes in skyglow. This is because satellites that observe Earth at night measure the light that is radiating into the sky, not the brightness that is experienced by people and other organisms on the ground. While models can use satellite data to provide estimates of how bright the sky is, these models need to be tested with data from around the world.

“Another drawback of the current night observing satellites is that they aren’t sensitive to certain wavelengths of light”, says Franz Hölker. “In particular, areas lit by new white LED lights appear darker from these instruments then they really are.”

The app can be downloaded free of charge, and is available in 15 languages (Arabic, Catalan, Chinese, Czech, English, French, German, Hebrew, Italian, Japanese, Polish, Romanian, Slovak, Spanish, and Turkish). While the app can be used at any time, the researchers only analyze data taken when the moon is set. The next moon free period runs from November 11-24.

“If you have cloudy skies this month, don’t despair” says Kyba. “The new version will use your location to figure out the next time you can take a measurement.”

Since 2013 the app has been only available for Android phones and was downloaded over 26,500 times. By improving the app and porting it to iOS, the scientists hope to encourage more citizen scientists to take part.